Industrial control systems have enabled modern factories to become partially or completely automated in many circumstances. These systems generally include a plurality of Input and Output (I/O) modules that interface at a device level to switches, contactors, relays and solenoids along with analog control to provide more complex functions such as Proportional, Integral and Derivative (PID) control. Communications have also been integrated within the systems, whereby many industrial controllers can communicate via network technologies such as Ethernet, Control Net, Device Net or other network protocols and also communicate to higher level computing systems. Generally, industrial controllers utilize the aforementioned technologies along with other technology to control, cooperate and communicate across multiple and diverse applications.
Conventional control systems employ a large array of varied technologies and/or devices to achieve automation of an industrial environment, such as a factory floor or a fabrication shop. Systems employed in an automated environment can utilize a plurality of sensors and feedback loops to direct a product through, for example, an automated assembly line. Such sensors can include temperature sensors (e.g., for determining a temperature of a steel bar that is entering a roller device to press the bar into a sheet . . . ), pressure sensors (e.g., for determining when a purge valve should be opened, for monitoring pressure in a hydraulic line . . . ), proximity sensors (e.g., for determining when an article of manufacture is present at a specific device and/or point of manufacture . . . ), etc.
Proximity sensors are available in a wide variety of configurations to meet a particular user's specific sensing needs. For example, sensors can be end-mounted in a housing, side-mounted in a housing, etc., to facilitate mounting in confined spaces while permitting the sensor to be directed toward a sensing region as deemed necessary by a designer. Additionally, proximity sensors are available with varied sensing ranges, and can be shielded or unshielded. Shielded inductive proximity sensors can be mounted flush with a surface and do not interfere with other inductive proximity sensors, but have diminished sensing range when compared with unshielded proximity sensors.
Of paramount importance in the field of proximity sensors is sensing distance, and, more specifically, increasing sensing distance. A problem often encountered when attempting to extend a sensing range of a proximity sensor is temperature drift, which can cause an error since the resistance change due to a target cannot be distinguished from a change due to temperature. Therefore, it is important to be able to compensate for this change in the coil resistance. For example, an uncompensated change of 1° C. can create an error of about 0.4% in the measurement of the coil resistance. For an extended range 18 mm diameter unshielded sensors with a sensing range of 20 mm, the change in the effective resistance of the coil due to the presence of a target is about 1%. Thus it is seen that a small error in temperature compensation limits the accuracy of the proximity sensor.
As industrial control systems become more complex and as system demands require finer-tuned sensing devices, so too does proximity sensor efficiency become ever more important. Thus, a need exists in the art for systems and methods that facilitate increasing efficiency of sensing devices and accounting for temperature effects on sensing coils in proximity sensors in an industrial automation environment.